The present invention relates to novel water-soluble block copolymers comprising polyoxyalkylene units and having crosslinkable side groups, to processes for their preparation, and to their use in the production of mouldings, especially contact lenses.
Polymers comprising polyalkylene oxide and having polymerisable end groups and their use in the production of contact lenses are already known, for example from EP-A-273 763.
Furthermore, there are known, for example from A. Kameyama et al. Macromol. 25, 2307 (1992), H. Itoh et al. Macromol. 28, 883 (1995) or H. Itoh et al. J. Pol. Sci. A, Pol. Chem. 34, 217 (1996), polyesters having chloromethyl side groups, polymers derived therefrom that have side groups comprising carboxy groups, and polyesters having vinyl ether side groups.
Surprisingly, novel crosslinkable polyether-polyester copolymers have now been found, which are suitable especially for the production of contact lenses.
The present invention relates to prepolymers comprising structural units of the formula 
Z is straight-chained or branched C1-C12alkylene or unsubstituted or C1-C4alkyl- or C1-C4-alkoxy-substituted phenylene or C7-C12aralkylene,
x and t are each independently of the other the number 0 or 1,
R5 is hydrogen, C1-C4alkyl or halogen,
R6 is hydrogen, C1-C4alkyl, phenyl, carboxy or halogen,
R7 is hydrogen when R6 is phenyl or carboxy, or is hydrogen or carboxy when R6 is hydrogen, C1-C4alkyl or halogen,
R8 is a C2-C12alkylene radical, a phenylene radical or a C7-C12aralkylene radical,
R9 and R9xe2x80x2 are each independently of the other hydrogen, C1-C4alkyl or halogen,
R1 is a radical of the formula
xe2x80x94[CH2xe2x80x94CHRxe2x80x3xe2x80x94O]nxe2x80x94CH2xe2x80x94CHRxe2x80x3xe2x80x94xe2x80x83xe2x80x83(3a) or
xe2x80x94[CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94O]nxe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94xe2x80x83xe2x80x83(3b);
xe2x80x83or an alkylene radical having up to 20 carbon atoms which may be interrupted by one or more ester, urethane or ureido groups and/or may be substituted by hydroxy; or a cycloalkylene radical having from 6 to 20 carbon atoms; or an arylene radical having from 6 to 20 carbon atoms; or an arylenealkylene, alkylenearylene, alkylenearylenealkylene or arylenealkylenearylene radical,
R2 is a radical of the formula
xe2x80x94CH2xe2x80x94[CH2xe2x80x94CHR*xe2x80x94O]pxe2x80x94CH2xe2x80x94xe2x80x83xe2x80x83(4) or
xe2x80x94R3xe2x80x94C(O)xe2x80x94[Oxe2x80x94CHR*xe2x80x94CH2]pxe2x80x94Oxe2x80x94(O)Cxe2x80x94R3xe2x80x94xe2x80x83xe2x80x83(5);
xe2x80x83or an alkylene radical having up to 20 carbon atoms which may be interrupted by one or more ester, urethane or ureido groups and/or may be substituted by hydroxy; or a cycloalkylene radical having from 6 to 20 carbon atoms; or an arylene radical having from 6 to 20 carbon atoms; or an arylenealkylene, alkylenearylene, alkylenearylenealkylene or arylenealkylenearylene radical,
Rxe2x80x2, Rxe2x80x3 and R* are each independently of the others hydrogen or C1-C4alkyl,
R3 is an alkylene radical having up to 20 carbon atoms; or a cycloalkylene radical having from 6 to 20 carbon atoms; or an arylene radical having from 6 to 20 carbon atoms, and n, m, p and q are each independently of the others a number from 1 to 30,
with the proviso that at least one of the radicals R1 and R2 is a radical of formula (3a), (3b), (4) or (5).
Z as an alkylene radical is preferably linear or branched C1-C8alkylene, especially linear C1-C4alkylene and more especially linear C1-C2alkylene. In a preferred embodiment of the invention, Z is methylene.
Z as a phenylene radical is, for example, unsubstituted or methyl- or methoxy-substituted 1,2-, 1,3- or 1,4-phenylene. Z as a phenylene radical is preferably 1,3- or 1,4-phenylene.
Z as an aralkylene radical is, for example, unsubstituted or methyl- or methoxy-substituted benzylene, the methylene group in each case being bonded to the amine nitrogen. Z as an aralkylene radical is preferably the 1,3- or 1,4-phenylenemethylene radical, the methylene group in each case being bonded to the amine nitrogen xe2x80x94NHxe2x80x94.
Z is preferably unsubstituted or methyl- or methoxy-substituted phenylene or phenylenemethylene or C1-C8alkylene, especially 1,3- or 1,4-phenylene or C1-C4alkylene, more especially C1-C2alkylene and most especially methylene.
x is preferably the number 0. t is preferably the number 1.
R5 is preferably hydrogen, C1-C4alkyl or chlorine, especially hydrogen or C1-C4alkyl, more especially hydrogen, methyl or ethyl and most especially hydrogen or methyl.
R6 is preferably hydrogen, methyl or phenyl and especially hydrogen.
R7 is preferably hydrogen.
R8 is preferably a C2-C6alkylene radical or a 1,3- or 1,4-phenylene radical, especially a C2-C3alkylene radical. R9 and R9xe2x80x2 are each independently of the other preferably hydrogen, methyl or chlorine. R9 and R9xe2x80x2 are each independently of the other especially hydrogen or methyl.
Each of Rxe2x80x2, Rxe2x80x3 and R* as C1-C4alkyl is preferably methyl or ethyl and especially methyl.
Rxe2x80x2 and Rxe2x80x3 are each independently of the other preferably hydrogen, methyl or ethyl and especially hydrogen or methyl.
R* is especially hydrogen or methyl and more especially hydrogen.
m is preferably a number from 1 to 6 and especially a number from 1 to 4. q is, for example, a number from 1 to 6, preferably a number from 2 to 4 and especially the number 2.
R in formula (1) is preferably a radical of the formula
xe2x80x94Oxe2x80x94(O)Cxe2x80x94CR5xe2x95x90CH2xe2x80x83xe2x80x83(2axe2x80x2) or
xe2x80x94Oxe2x80x94(O)Cxe2x80x94(CH2)mxe2x80x94Oxe2x80x94(O)Cxe2x80x94NHxe2x80x94(CH2)qxe2x80x94Oxe2x80x94(O)Cxe2x80x94CRxe2x80x2xe2x95x90CH2xe2x80x83xe2x80x83(2bxe2x80x2),
wherein the variables contained therein each have the meanings and preferred meanings indicated above.
In an especially preferred embodiment of the invention, R in formula (1) is a radical of formula (2axe2x80x2) indicated above wherein R5 is hydrogen or methyl.
In formulae (3a) and (3b), n is, for example, a number from 5 to 30, advantageously from 5 to 25, preferably from 8 to 25 and especially from 10 to 25.
When R1 is an alkylene radical it is, for example, straight-chained or branched C1-C20-alkylene which is unsubstituted or substituted, for example by hydroxy, and/or, with the exception of methylene, may be interrupted by one or more groups xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94NHCOxe2x80x94Oxe2x80x94, xe2x80x94OCONHxe2x80x94 or xe2x80x94NHCONHxe2x80x94. R1 as an alkylene radical is preferably unsubstituted or hydroxy-substituted C1-C20alkylene, especially unsubstituted C1-C12alkylene and more especially unsubstituted C1-C6alkylene. Examples of alkylene radicals R1 that are very especially preferred are methylene, 1,2-ethylene, 1,3-propylene and 1,4-butylene.
R1 as cycloalkylene is, for example, 1,2-, 1,3- or 1,4-cyclohexylene which may be substituted by C1-C4alkylene, or is a radical of the formula 
R1 as arylene is, for example, 1,2-, 1,3- or 1,4-phenylene which is unsubstituted or is substituted by C1-C4alkyl, C1-C4alkoxy or by halogen, or is a radical of the formula 
wherein B is, for example, a group xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONHxe2x80x94 or xe2x80x94NHCONHxe2x80x94. R1 as arylene is preferably 1,2-, 1,3- or 1,4-phenylene.
R1 as arylenealkylene, alkylenearylene or alkylenearylenealkylene is, for example, a radical xe2x80x94C6H5xe2x80x94C1-C4alkylenexe2x80x94, xe2x80x94C1-C4alkylene-C6H5xe2x80x94 or xe2x80x94C1-C4alkylene-C6H5xe2x80x94C1-C4alkylene, preferably the radical xe2x80x94C6H5xe2x80x94CH2xe2x80x94, xe2x80x94CH2xe2x80x94C6H5xe2x80x94 or xe2x80x94CH2xe2x80x94C6H5xe2x80x94CH2xe2x80x94.
R1 as arylenealkylenearylene is, for example, a radical of the formula 
wherein B1 is straight-chained or branched C1-C6alkylene which is unsubstituted or is substituted by hydroxy, preferably straight-chained or branched C1-C4alkylene. Examples of suitable radicals B1 are xe2x80x94CH2xe2x80x94, xe2x80x94C(CH3)2xe2x80x94 and xe2x80x94CH2xe2x80x94CH2xe2x80x94.
R1 is advantageously a radical of formula (3a) or (3b) indicated above, or C1-C20alkylene, 1,2-, 1,3- or 1,4-phenylene or a radical of the formula 
wherein B1 is straight-chained or branched C1-C4alkylene.
R1 is preferably a radical of formula (3a) indicated above, or C1-C20alkylene, especially a radical of formula (3a) indicated above wherein n is a number from 5 to 25 and Rxe2x80x3 is hydrogen or methyl, or C1-C12alkylene, and more especially a radical of formula (3a) indicated above wherein n is a number from 8 to 25 and Rxe2x80x3 is hydrogen or methyl, or C1-C6-alkylene.
In formulae (4) and (5), p is preferably a number from 5 to 25, especially from 8 to 25 and more especially from 10 to 25.
R3 as an alkylene radical is preferably straight-chained or branched C1-C12alkylene, especially straight-chained or branched C1-C6alkylene and more especially straight-chained or branched C1-C4alkylene. Examples of alkylene radicals R4 that are very especially preferred are methylene, 1,2-ethylene, 1,3-propylene and 1,4-butylene.
When R3 is a cycloalkylene or arylene radical, the definitions and preferred meanings mentioned above for R2 apply independently.
R3 is preferably a straight-chained C1-C4alkylene radical.
When R2 is an alkylene, cycloalkylene, arylene, arylenealkylene, alkylenearylene, alkylenearylenealkylene or arylenealkylenearylene radical, the definitions and preferred meanings given above for R1 apply independently.
R2 is preferably a radical of formula (4) or (5) indicated above, or C1-C20alkylene, 1,2-, 1,3- or 1,4-phenylene or a radical of the formula 
wherein B1 is straight-chained or branched C1-C4alkylene. R2 is especially a radical of formula (4) indicated above, or C1-C20alkylene, more especially a radical of formula (4) indicated above wherein p is a number from 5 to 25 and R* is hydrogen or methyl, or C1-C12alkylene, and most especially a radical of formula (4) indicated above wherein p is a number from 8 to 25 and Rxe2x80x3 is hydrogen, or C1-C6alkylene.
A preferred embodiment of the present invention relates to prepolymers comprising structural units of formula (1) indicated above wherein R1 is a radical of formula (3a) indicated above and R2 is a C1-C20alkylene radical. Special preference is given to such polymers in which R1 is a radical of formula (3a) indicated above wherein n is a number from 5 to 25 and Rxe2x80x3 is hydrogen or methyl, and R2 is C1-C6alkylene.
Another preferred embodiment of the present invention relates to prepolymers comprising structural units of formula (1) indicated above wherein R1 is a C1-C20alkylene radical and R2 is a radical of formula (4) indicated above. Special preference is given to such polymers in which R1 is C1-C6alkylene and R2 is a radical of formula (4) indicated above wherein p is a number from 5 to 25 and R* is hydrogen.
Another preferred embodiment of the present invention relates to prepolymers comprising structural units of formula (1) indicated above wherein the above-mentioned definitions and preferred meanings apply to each of R1 and R2, and R is the acrylate or methacrylate radical xe2x80x94O(O)Cxe2x80x94CHxe2x95x90CH2 or xe2x80x94O(O)Cxe2x80x94C(CH3)xe2x95x90CH2.
In addition to the structural units of formula (1) mentioned above, the prepolymers of the invention may comprise, for example, structural units of the formula 
wherein R0 is halogen or a radical xe2x80x94Oxe2x80x94(O)Cxe2x80x94R4 and R4 is C1-C20alkyl, C6-C20cycloalkylene, C6-C20arylene or C7-C12aralkylene.
When R0 is halogen, it may be, for example, fluorine, bromine, iodine or, especially, chlorine.
R4 as alkyl is, for example, a straight-chained or branched C1-C20alkyl radical which is unsubstituted or is substituted by hydroxy, preferably a straight-chained or branched C1-C12alkyl radical and especially a straight-chained or branched C1-C6alkyl radical. Examples are methyl, ethyl, n- or iso-propyl, n-, iso-, sec- or tert-butyl or straight-chained or branched pentyl or hexyl and, especially, methyl or ethyl.
R4 as cycloalkyl is, for example, unsubstituted or C1-C4alkyl-substituted cyclohexyl, preferably cyclohexyl which is unsubstituted or is substituted by from 1 to 3 methyl groups, and especially unsubstituted cyclohexyl.
R4 as aryl is, for example, phenyl which is unsubstituted or is substituted by halogen, hydroxy, carboxy, C1-C4alkyl or by C1-C4alkoxy, preferably phenyl which is unsubstituted or is substituted by chlorine, methyl, methoxy or by carboxy, and especially unsubstituted phenyl.
R4 as aralkyl is, for example, phenylmethyl or phenylethyl.
R4 is preferably C1-C12alkyl, cyclohexyl which is unsubstituted or is substituted by from 1 to 3 methyl groups, phenyl which is unsubstituted or is substituted by chlorine, methyl, methoxy or by carboxy, or phenylmethyl or phenylethyl.
R4 is especially C1-C6alkyl, cyclohexyl or phenyl.
Preferred constituents of the prepolymers of the invention are those units of formula (1a) wherein R0 is chlorine or a radical xe2x80x94Oxe2x80x94(O)Cxe2x80x94R4 and R4 is C1-C6alkyl, cyclohexyl or phenyl.
The crosslinkable prepolymers of the invention comprise, for example, from 100 to 60 mol. % of units of formula (1) and from 0 to 40 mol. % of units of formula (1a). Preference is given to such polymers that comprise from 100 to 80 mol. % of units of formula (1) and from 0 to 20 mol. % of units of formula (1a).
The crosslinkable prepolymers of the invention can be prepared, for example, by
(a) polymerising a compound of the formula 
xe2x80x83with a compound of the formula
X(O)Cxe2x80x94R2xe2x80x94C(O)Xxe2x80x83xe2x80x83(7)
xe2x80x83in the presence of a catalyst, and
(b) reacting the polymer obtainable according to (a), which comprises structural units of the formula 
xe2x80x83with a compound of the formula
Rxe2x80x94Hxe2x80x83xe2x80x83(8)
xe2x80x83in the presence of a base, R1 and R2 each being as defined above, X being halogen, preferably chlorine, and R being a radical of formula (2a), (2c), (2d) or (2b) indicated above wherein t is the number 1.
The compounds of formula (1) wherein R is a radical of formula (2b) and t is the number 0 can be obtained, for example, by converting a polymer of formula (1a) prepared in the manner described above into a corresponding polymer wherein X is hydroxy and reacting the latter with an isocyanate of the formula Oxe2x95x90Cxe2x95x90Nxe2x80x94(CH2)qxe2x80x94Oxe2x80x94(O)Cxe2x80x94CHRxe2x80x2xe2x95x90CH2 wherein Rxe2x80x2 and q are as defined above.
The reaction of the diacid dihalide with the diglycidyl compound to form a polyester according to step (a) is known per se and can be carried out by methods known per se. The reaction of the acid dihalide with the diglycidyl compound is usually carried out in an inert solvent, for example in a higher-boiling alkane or alkane mixture, such as petroleum ether, in a xylene mixture or in toluene, at elevated temperature, for example at from 30 to 120xc2x0 C., preferably from 40 to 100xc2x0 C. and especially from 60 to 100xc2x0 C., in the presence of a basic catalyst.
Suitable catalysts are, for example, crown ether complexes, pyridine, quaternary phosphonium salts, tertiary amines or, preferably, quaternary ammonium salts. Examples of suitable catalysts are pyridine, tri-C1-C4alkylamines, especially tributylamine, and tetra-C1-C4alkyl-ammonium halides, especially tetrabutylammonium halides, such as tetrabutylammonium chloride, tetrabutylammonium iodide or, especially, tetrabutylammonium bromide.
The catalyst is used in the polymerisation reaction, for example, in a molar ratio of from 1:10 to 1:50, preferably from 1:15 to 1:30 and especially of about 1:20, in each case based on the diacid dihalide. The molar ratio of diglycidyl compound to diacid dihalide can vary, for example, from 0.5:1 to 2:1 and is preferably about 1:1.
The reaction of the halide-group-containing polyester obtainable according to (a) with the carboxylic acid of formula (8) is advantageously carried out at elevated temperature, for example at from 30 to 100xc2x0 C., preferably from 40 to 100xc2x0 C. and especially from 60 to 90xc2x0 C., in an aprotic-dipolar solvent, for example in DMSO, in the presence of a base, 1,8-diaza-bicyclo[5.4.0]undec-7-ene (DBU) having proved especially advantageous. The acid is used in a molar excess, based on the halide-group-containing polymer, and the base is advantageously present in about equimolar amounts, based on the acid of formula (8).
Depending on the chosen stoichiometric ratios and reaction conditions, the prepolymer of the invention obtainable after isolation in customary manner consists essentially of structural units of formula (1) indicated above or comprises, in addition to the structural units of formula (1), structural units of formula (1a) indicated above wherein R0 is halogen. If step (b) is carried out using a mixture of an acid of formula (8) indicated above and an acid of the formula
R4xe2x80x94C(O)xe2x80x94Oxe2x80x94Hxe2x80x83xe2x80x83(9)
wherein R4 is as defined above, the prepolymer comprises a mixture of structural units of formula (1), structural units of formula (1a) wherein R0 is a radical xe2x80x94Oxe2x80x94(O)Cxe2x80x94R4, and, where appropriate, structural units of formula (1a) wherein R0 is halogen.
The prepolymers of the invention are crosslinkable but are uncrosslinked or at least substantially uncrosslinked; moreover, they are stable, that is to say spontaneous crosslinking by homopolymerisation does not take place.
The prepolymers of the invention are advantageously liquid or readily meltable or water-soluble; their average molecular weight can vary within wide limits. An average molecular weight of, for example, from 1000 to 20 000 has proved advantageous for the prepolymers of the invention.
Furthermore, the prepolymers comprising structural units of formula (1) and, where appropriate, (1a) can be purified in a manner known per se, for example by precipitation with acetone, dialysis or ultrafiltration, with ultrafiltration being especially preferred. By means of that purification process it is possible to obtain the prepolymers of the invention in an extremely pure form, for example in the form of solvent-free liquids or melts or in the form of concentrated aqueous solutions that are free or at least substantially free of reaction products, such as salts, and of starting materials or other non-polymeric constituents.
The preferred process for purifying the prepolymers of the invention, ultrafiltration, can be carried out in a manner known per se. It is possible to carry out the ultrafiltration repeatedly, for example from two to ten times. Alternatively, the ultrafiltration can be carried out continuously until the desired degree of purity has been achieved. The degree of purity can in principle be as high as desired and is preferably so adjusted that the content of undesirable constituents in the prepolymers is, for example, xe2x89xa60.001%, especially xe2x89xa60.0001% (1 ppm). The prepolymers may, for example depending on their synthesis, comprise in addition constituents that are acceptable from a physiological point of view, for example sodium chloride, such constituents advantageously being present in an amount of xe2x89xa61%, preferably xe2x89xa60.1% and especially xe2x89xa60.01%.
As has already been mentioned above, the prepolymers of the invention comprising structural units of formula (1) and, where appropriate, (1a) are crosslinkable in an extremely effective and specific manner, especially by means of photocrosslinking.
Accordingly, the present invention relates also to a polymer that can be obtained by photocrosslinking a prepolymer comprising units of formula (1) and, where appropriate, (1a), in the absence or presence of an additional vinyl comonomer. Those crosslinked polymers are insoluble in water.
In the photocrosslinking, a photoinitiator capable of initiating radical crosslinking is suitably added. Examples thereof are known to the person skilled in the art, but there may be mentioned specifically as suitable photoinitiators benzoin methyl ether, 1-hydroxycyclohexyl phenyl ketone, Darocure 1173 or Irgacure types. Crosslinking can then be induced by actinic radiation, for example UV light, or ionising radiation, for example gamma radiation or X-rays.
Photopolymerisation can be carried out without the addition of a solvent, for example when the prepolymer is liquid or readily meltable, or takes place in a suitable solvent. Suitable solvents are in principle any solvents that dissolve the polymers of the invention and the vinyl comonomers that may additionally be used, for example water, alcohols, such as lower alkanols, for example ethanol or methanol, also carboxylic acid amides, such as dimethyl-formamide, or dimethyl sulfoxide, as well as mixtures of suitable solvents, for example mixtures of water with an alcohol, for example a water/ethanol or water/methanol mixture.
Photocrosslinking is preferably carried out without a solvent or substantially without a solvent or directly from an aqueous solution of the prepolymers of the invention (which solution can be obtained as a result of the preferred purification step, ultrafiltration), where appropriate after the addition of an additional vinyl comonomer. For example, photocrosslinking of an approximately 15 to 90% strength aqueous solution can be carried out.
The process for the preparation of the crosslinked polymers of the invention comprises, for example, photocrosslinking a prepolymer comprising units of formula (1) and, where appropriate, (1a), especially in substantially pure form, that is to say, for example, after ultra-filtration once or several times, without a solvent or substantially without a solvent or in solution, especially in an aqueous solution, in the absence or presence of an additional vinyl comonomer.
The vinyl comonomer that may additionally be used according to the invention in the photocrosslinking may be hydrophilic, hydrophobic or a mixture of a hydrophobic and a hydrophilic vinyl monomer. Suitable vinyl monomers include especially those which are customarily used in the production of contact lenses. A hydrophilic vinyl monomer is understood as being a monomer that, as a homopolymer, typically yields a polymer that is water-soluble or can absorb at least 10% by weight water. By analogy, a hydrophobic vinyl monomer is understood as being a monomer that, as a homopolymer, typically yields a polymer that is insoluble in water and can absorb less than 10% by weight water.
In general, approximately from 0.01 to 80 units of a typical vinyl comonomer react per unit of formula (1) and, as the case may be, (1a).
The proportion of vinyl comonomers, where used, is preferably from 0.5 to 80 units per unit of formula (1), especially from 1 to 30 units of vinyl comonomer per unit of formula (1) and more especially from 5 to 20 units per unit of formula (1).
It is further preferred to use a hydrophobic vinyl comonomer or a mixture of a hydrophobic vinyl comonomer and a hydrophilic vinyl comonomer, the mixture containing at least 50% by weight of a hydrophobic vinyl comonomer. In this manner, the mechanical properties of the polymer can be improved without the water content dropping substantially. In principle, however, both conventional hydrophobic vinyl comonomers and conventional hydrophilic vinyl comonomers are suitable for the copolymerisation with a prepolymer comprising groups of formula (1).
Suitable hydrophobic vinyl comonomers include the following, this list not being exhaustive: C1-C18alkyl acrylates and methacrylates, C3-C18alkyl-acrylamides and -methacrylamides, acrylonitrile, methacrylonitrile, vinyl C1-C18alkanoates, C2-C18alkenes, C2-C18haloalkenes, styrene, C1-C6alkylstyrene, vinyl alkyl ethers in which the alkyl moiety has from 1 to 6 carbon atoms, C2-C10perfluoroalkyl acrylates and methacrylates or correspondingly partially fluorinated acrylates and methacrylates, C3-C12perfluoroalkyl-ethyl-thiocarbonylaminoethyl acrylates and methacrylates, acryloxy- and methacryloxy-alkylsiloxanes, N-vinylcarbazole, C1-C12alkyl esters of maleic acid, fumaric acid, itaconic acid, mesaconic acid and the like. Preference is given, for example, to C1-C4alkyl esters of vinylically unsaturated carboxylic acids having from 3 to 5 carbon atoms or vinyl esters of carboxylic acids having up to 5 carbon atoms.
Examples of suitable hydrophobic vinyl comonomers include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, styrene, chloroprene, vinyl chloride, vinylidene chloride, acrylonitrile, 1-butene, butadiene, methacrylonitrile, vinyltoluene, vinyl ethyl ether, perfluorohexylethylthiocarbonylaminoethyl methacrylate, isobornyl methacrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, hexafluorobutyl methacrylate, tris-trimethylsilytoxy-silyl-propyl methacrylate, 3-methacryloxypropylpentamethyidisiloxane and bis(methacryloxypropyl)tetramethyidisiloxane.
Suitable hydrophilic vinyl comonomers include the following, this list not being exhaustive: hydroxy-substituted lower alkyl acrylates and methacrylates, acrylamide, methacrylamide, lower alkyl acrylamides and methacrylamides, ethoxylated acrylates and methacrylates, hydroxy-substituted lower alkyl-acrylamides and -methacrylamides, hydroxy-substituted lower alkyl vinyl ethers, sodium ethylenesulfonate, sodium styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrole, N-vinylsuccinimide, N-vinylpyrrolidone, 2- or 4-vinylpyridine, acrylic acid, methacrylic acid, amino- (the term xe2x80x9caminoxe2x80x9d also including quaternary ammonium), mono-lower alkylamino- or di-lower alkylamino-lower alkyl acrylates and methacrylates, allyl alcohol and the like. Preference is given, for example, to hydroxy-substituted C2-C4alkyl (meth)acrylates, five- to seven-membered N-vinyllactams, N,N-di-C1-C4alkyl(meth)acrylamides, and vinylically unsaturated carboxylic acids having a total of from 3 to 5 carbon atoms.
Examples of suitable hydrophilic vinyl comonomers include hydroxyethyl methacrylate, hydroxyethyl acrylate, acrylamide, methacrylamide, dimethylacrylamide, allyl alcohol, vinylpyridine, vinylpyrrolidone, glycerol methacrylate, N-(1,1-dimethyl-3-oxobutyl)acrylamide and the like.
Preferred hydrophobic vinyl comonomers are methyl methacrylate and vinyl acetate.
Preferred hydrophilic vinyl comonomers are 2-hydroxyethyl methacrylate, N-vinyl-pyrrolidone and acrylamide.
The prepolymers of the invention can be processed in a manner known per se to form mouldings, especially contact lenses, for example by carrying out the photocrosslinking of the prepolymers of the invention in a suitable contact lens mould. Accordingly, the invention relates also to mouldings consisting essentially of a prepolymer of the invention. Other examples of mouldings of the invention, in addition to contact lenses, are biomedical mouldings and, especially, ophthalmic mouldings, for example intraocular lenses, eye dressings, mouldings for use in surgery, such as heart valves, artificial arteries or the like, and also films or membranes, for example membranes for controlling diffusion, photostructurable foils for information storage, or photoresist materials, for example membranes or mouldings for etching resist or screen printing resist.
A preferred process for the production of mouldings comprises the following steps:
a) introducing into a mould a prepolymer comprising structural units of formula (1) and, where appropriate, (1a) that is liquid at room temperature or is readily meltable and is substantially free of solvents, in the absence or presence of an additional vinyl comonomer and/or photoinitiator,
b) inducing the photocrosslinking,
c) opening the mould so that the moulding can be removed from the mould.
Another preferred process for the production of mouldings comprises the following steps:
a) preparing a substantially aqueous solution of a water-soluble prepolymer comprising structural units of formula (1) and, where appropriate, (1a) in the absence or presence of an additional vinyl comonomer and/or photoinitiator,
b) introducing the resulting solution into a mould,
c) inducing the photocrosslinking,
d) opening the mould so that the moulding can be removed from the mould.
In the preferred processes outlined above it is in each case especially preferred to introduce the prepolymer into the mould in the absence of an additional vinyl comonomer and in the presence of a photoinitiator.
For the introduction of the prepolymers of the invention into a mould, processes known per se can be used, such as, especially, conventional metering in, for example by means of dropwise introduction. If vinyl comonomers are present, the above-mentioned comonomers in the amounts mentioned there are suitable. Vinyl comonomers that may be present are advantageously first mixed with the prepolymer of the invention and then introduced into the mould.
Appropriate moulds are manufactured, for example, from polypropylene. Suitable materials for reusable moulds are, for example, quartz, sapphire glass or metals.
When the mouldings to be produced are contact lenses, they can be produced in a manner known per se, for example in a conventional xe2x80x9cspin-casting moldxe2x80x9d, as described, for example, in U.S. Pat. No. 3,408,429, or by the so-called full-mold process in a static mould, as described, for example, in U.S. Pat. No. 4,347,198.
The photocrosslinking can be induced in the mould, for example by actinic radiation, e.g. UV light, or ionising radiation, e.g. gamma radiation or X-rays.
As has already been mentioned, the photocrosslinking is advantageously carried out in the presence of a photoinitiator capable of intitiating radical crosslinking. The photoinitiator is advantageously added to the prepolymers of the invention before introduction into the mould, preferably by mixing the polymers and the photoinitiator together. The amount of photoinitiator can be chosen within wide limits, an amount of up to 0.05 g/g of polymer and especially of up to 0.003 g/g of polymer having proved advantageous.
It is to be emphasised that according to the invention the crosslinking can be effected in a very short time, for example in xe2x89xa660 minutes, advantageously in xe2x89xa620 minutes, preferably in xe2x89xa610 minutes, especially in xe2x89xa65 minutes, more especially in xe2x89xa61 minute and most especially in xe2x89xa630 seconds.
Opening of the mould so that the moulding can be removed from the mould can be carried out in a manner known per se.
When the moulding produced according to the invention is a contact lens and when the latter has been produced without a solvent from a previously purified prepolymer of the invention, then it is generally not necessary, after removing the moulding, to carry out subsequent purification steps, for example extraction. This is because the prepolymers used do not contain any undesirable low-molecular-weight constituents; consequently, the crosslinked product is also free or substantially free of such constituents and subsequent extraction is unnecessary. Accordingly, the contact lens can be converted directly into a ready-to-use contact lens in customary manner by hydration. Suitable forms of hydration, by means of which ready-to-use contact lenses having different water contents are obtainable, are known to the person skilled in the art. The contact lens is swelled, for example, in water, in an aqueous salt solution, especially in an aqueous salt solution having an osmolarity of approximately from 200 to 450 milliosmol in 1000 ml (unit: mOsm/l), preferably approximately from 250 to 350 mOsm/l and especially approximately 300 mOsm/l, or in a mixture of water or an aqueous salt solution with a physiologically tolerable polar organic solvent, for example glycerol. Swelling of the prepolymer in water or in aqueous salt solutions is preferred.
The aqueous salt solutions used for the hydration are advantageously solutions of physiologically tolerable salts, such as buffer salts that are customary in the field of contact lens care, for example phosphate salts, or agents for establishing isotonicity that are customary in the field of contact lens care, such as, especially, alkali metal halides, for example sodium chloride, or solutions of mixtures thereof. An example of an especially suitable salt solution is a synthetic, preferably buffered lachrymal fluid that is adapted to natural lachrymal fluid as regards pH and osmolarity, for example an unbuffered sodium chloride solution, preferably a sodium chloride solution that is buffered, for example buffered with phosphate buffers, and the osmolarity and pH of which correspond to the osmolarity and pH of human lachrymal fluid.
The hydration fluids defined above are preferably pure, that is to say free or substantially free of undesirable constituents. Special preference is given to pure water or to a synthetic lachrymal fluid as described above.
When the moulding produced according to the invention is a contact lens and when the latter has been produced from an aqueous solution of a previously purified prepolymer of the invention, then the crosslinked product does not contain any troublesome impurities either. Subsequent extraction is therefore unnecessary. Since the crosslinking is carried out in a substantially aqueous solution, subsequent hydration is also unnecessary. The contact lenses obtainable according to that process are therefore distinguished, according to an advantageous embodiment, by the fact that they are suitable for their designated use without extraction. In this connection, designated use is understood as meaning especially that the contact lenses can be inserted into the human eye.
The contact lenses obtainable according to the invention have a range of unusual and extremely advantageous properties. Of those properties there may be mentioned, for example, their excellent tolerability by the human cornea, which is based on a balance of water content, oxygen permeability and mechanical properties. Moreover, the contact lenses of the invention exhibit a high degree of dimensional stability. No changes in shape were discernible even after autoclaving at, for example, about 120xc2x0 C.
It can also be emphasised that the contact lenses of the invention, that is to say especially those comprising a crosslinked polymer of a prepolymer comprising units of formula (1) and, where appropriate, (1a), can be produced in a very simple and efficient manner as compared with the prior art. This is the result of several factors. Firstly, the starting materials are inexpensive to obtain or prepare. Secondly, there is the advantage that the prepolymers are surprisingly stable, so that they can be subjected to a high degree of purification. Accordingly, it is possible to use for the crosslinking a polymer that requires virtually no subsequent purification, such as, especially, the complicated extraction of unpolymerised constituents. Moreover, the crosslinking can be carried out without a solvent or in an aqueous solution, so that the subsequent exchange of solvents or the hydration step, respectively, is not required. Finally, the photopolymerisation takes place in a short time, so that the process for the production of the contact lenses of the invention can be made extraordinarily economical from that point of view also.
All the advantages mentioned above naturally apply not only to contact lenses but also to other mouldings according to the invention. The sum of the various advantageous aspects in the production of the mouldings of the invention leads to the mouldings of the invention being suitable especially as mass-produced articles, for example as contact lenses that are worn for a short period of time and are then replaced by new lenses.
In the Examples which follow, unless expressly indicated to the contrary, quantities are by weight and temperatures are given in degrees Celsius. Unless indicated otherwise, molecular weights Mn are determined by means of gel permeation chromatography (GPC) [size exclusion chromatography (SEC)] using DMF as solvent, and are related to the calibration standard of polymethyl methacrylate (PMMA).